The present invention relates to a fuel tank and, more particularly, to a fuel tank for a motor vehicle which includes two shaped shells. Each of the shaped shells includes a shell bottom, shell walls, and a continuous circumferential shell rim. The shell rims of each shaped shell are adapted to be abutted and welded together thereby forming a closed fuel tank or cell. At least one of the shaped shells utilized in the formation of the fuel tank includes reinforcing ribs which are arranged, with respect to their direction, generally perpendicularly relative to a rim portion extending generally parallel to the bottom of the composite structure forming the fuel tank.
Fuel tanks are typically under a compressive and weight load due to the fluid accommodated in the tank, the result of which leads to stresses in the container wall or walls, particularly, during acceleration and braking of the motor vehicle. Pressure fluctuations are produced in the tank by the fuel causing additional stresses in the tank walls. Thus, stress peaks are created by an overlapping or super position of stresses, the highest of which are at or near the bottom of the tank, and which may cause undesirable deformation of the tank walls. Historically, the approach has been to construct the fuel tank in a manner such that the tank walls are form rigid and dimensionally stable so that stresses are absorbed by the tank walls.
In prior art fuel tanks which are generally of the aforementioned type, i.e., of two form rigid formed shell-like parts welded together along complementary rims, an uneven or non-uniform stress distribution occurs in the shell walls proximate the bottom area of the composite tank and in the welded seam when the fuel tank contains a substantial quantity of fuel therein. This usually is due to the existence of reinforcing ribs arranged in the shell-like parts, as a result of which the walls are deformed, leading to the formation of cracks because of the occurrence of shear forces, in an area between the shell walls and the rigid welded seam.
An approach to preventing the formation of cracks and the deformation of the shell walls has been to provide a wall thickness for the tank which would be sufficient to absorb the stress peaks. However, this approach typically results in a massive fuel tank which requires a considerable amount of material having a considerable weight.
Another previous approach to the above-identified problem has been to provide fuel tanks with straps which in turn lend stability to the tank. While it is understood that straps will in fact reduce the deformation of the walls of the tank, it is also understood that such an approach requires additional assembly and consequently additional expenditure.